While there is a continuing demand for a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, active efforts have been devoted to develop the microfabrication technology utilizing deep- and vacuum-ultraviolet lithography. In particular, the ArF excimer laser (193 nm) is widely acknowledged as a light source of next generation to the KrF excimer laser and used in photolithography processing advanced semiconductor devices of 90 nm node and forward. While poly-p-hydroxystyrene derivatives played a main role as the base resin in resist compositions of the KrF excimer laser generation, they are difficultly applicable to the photolithography using the ArF excimer laser as the light source because they are opaque to wavelength 193 nm. For the ArF excimer laser photolithography, it is the key factor to search for base resins having transparency.
Poly(meth)acrylic acid and derivatives thereof were considered attractive as the resins which are fully transparent at 193 nm and have relatively satisfactory development properties, but left a problem of dry etching resistance. For improving dry etching resistance, poly(meth)acrylate derivatives having alicyclic structures such as adamantane and norbornane structures incorporated in the pendant ester moiety were developed as described in JP-A 4-39665 and JP-A 5-257281. They became the main stream of development work.
These derivatives, however, are still insufficient in etching resistance. It is expected from the future pattern miniaturization trend that etching resistance will become a factor of more significance because formation of a thinner film of resist is essential to acquire a resolution.
Also proposed in the art are resins having an alicyclic structure as the backbone, for example, polynorbornene derivatives and alternating copolymers of polynorbornene derivatives and maleic anhydride. Although some have sufficient etching resistance, there remains unsolved the problem of poor resolution due to inferior development properties, i.e., swelling and low dissolution contrast during development.
Under these circumstances, a hydrogenated product of ring-opening metathesis polymerization (ROMP) polymer was proposed as meeting high levels of etching resistance and resolution (see JP-A 2002-202609). The hydrogenated ROMP polymer has superior etching resistance to the (meth)acrylate polymers due to an alicyclic skeleton in its backbone and also exhibits good development properties and hence good resolution probably due to a high mobility as compared with other alicyclic polymers. This polymer is thus quite advantageous as the base resin in ArF resist compositions.
Nevertheless, preparation of hydrogenated ROMP polymers requires a high precision level of polymerization and catalyst technology, from which several problems are raised. For example, high purity monomers which are indispensable to polymerization are difficult to prepare, and some monomers having certain functional groups are not susceptible to polymerization. Thus, the monomers which can be used in industrial polymerization are limited to certain structures. In addition, since customers currently have a wide diversity of demands, a wide variety of base resins are necessary to meet such demands. In the case of hydrogenated ROMP polymers, costly labors are needed in the manufacture of a wide variety of polymers because the overall preparation process is relatively long and includes steps each requiring a precise operation.